This is a basic story that proceeds how you think it'd proceed about a small fishing town than takes care of a mermaid egg. There is no twist of the plot or anything just the typical, town with mystical item gets besieged by corporate men and there's a race to return the item to wherever it needs to go.
All with a healthy dose of Casual Misogyny. Seriously it seems like Satoshi Kon hates women as they don't feature really prominently in this manga and only live to further the male plotline. Even the mermaid is rather nondescript.
Also I though this would be a novel which is the only reason I bought it, low and behold it's not and it's from Vertical. The people that don't know a thing about their properties.